Humidity change rate control in intermittently heated historic buildings

¹ Dept. Art History, Conservation, Uppsala University, Cramérgatan 3, 62153 Visby, Sweden
² Dept. Instrumentation and Control Eng., Faculty of Mechanical Eng., Czech Technical University in Prague, Technická 4, Prague 6, 166 07, Czech Republic

^* Corresponding author: magnus.wessberg@konstvet.uu.se

Abstract

Many massive historic buildings such as stone churches are intermittently heated. The predominant heating strategy is to heat the building with as high heating power as possible to achieve a fast and energy efficient heat-up process. However, the fast change rate of temperature induces a high change rate of relative humidity, which can be dangerous for interiors and objects in churches. It has been suggested that the change rate of relative humidity should be limited with respect to conservation. Desorption from the walls has a significant effect on the change rate of relative humidity. Typically, the absolute humidity can increase by 50% when the church is heated. Based on a hygrothermal model that allows for a prediction of both temperature and absolute humidity as function of time, this paper presents a model-based feed-forward control algorithm that calculates the maximum hourly heating power increase allowed for limit the change rate in relative humidity to a pre-defined value. The control algorithm is validated using simulations.